This invention relates to a pressure sensitive adhesive sheet and a pressure sensitive adhesive sheet with a release sheet.
Hard disk drives are widely used as a computer peripheral equipment.
In these hard disk drives, pressure sensitive adhesive sheets are attached for various purposes, such as temporary fixation of parts during manufacturing process, indication of the contents, inspection and closing of holes formed in a main body or a cover, and the like.
Such a pressure sensitive adhesive sheet is generally composed of a pressure sensitive adhesive sheet base and a pressure sensitive adhesive layer provided on the base, and it is being adhered to a release sheet until it is attached to a hard disk drive or the like.
On a surface of the release sheet (a surface to be attached to the pressure sensitive adhesive layer of the pressure sensitive adhesive sheet), a releasing agent layer is provided for improving reliability. Conventionally, a silicone resin has been used as a material of this releasing agent layer.
However, it is known that when such a release sheet is attached to a pressure sensitive adhesive sheet, silicone compound such as low molecular weight silicone resin, siloxane, or silicone oil contained in the releasing agent layer of the release sheet is transferred into the pressure sensitive adhesive layer of the pressure sensitive adhesive sheet. Further, normally, the release sheet is wound up in a rolled form after the production thereof, and in this state, the back surface of the release sheet is in contact with the releasing agent layer thereof, so that the silicone compound contained in the releasing agent layer is transferred to the back surface of the release sheet. In this regard, it is also known that the silicone compound transferred to the back surface of the release sheet is again transferred to the surface of a pressure sensitive adhesive sheet when winding up a pressure sensitive adhesive sheet with a release sheet (which is composed of a pressure sensitive adhesive sheet and a release sheet attached thereto) in a rolled form in manufacturing the pressure sensitive adhesive sheet with a release sheet. For this reason, it is also known that, when the pressure sensitive adhesive sheet to which such a release sheet has been adhered is attached to a hard disk drive, the silicone compound which has been transferred to the pressure sensitive adhesive layer or the surface of the pressure sensitive adhesive sheet gradually gasifiers, and then the gasified silicone compound deposits on a magnetic head, a disk surface or the like, thereby forming a fine silicone compound layer.
Further, in the case where general wood free paper, clay-coated paper or synthetic paper is used as a base of a pressure sensitive adhesive sheet or a release sheet, particles such as clay or dust of paper are generated from the base of the pressure sensitive adhesive sheet.
Meanwhile, in recent years, high performance and high density hard disc drives have been developed in a very short period of time, and it is believed that the tendency of seeking such high performance and high density will continue after this. If the tendency of such high performance and high density of hard disk drives continues further, there is the possibility that deposition of the silicone compound and deposition of the particles generated from the pressure sensitive adhesive sheet or release sheet give rise to adverse effects for reading and writing of data.
An object of the present invention is to provide a pressure sensitive adhesive sheet and a pressure sensitive adhesive sheet with a release sheet which are hard to give adverse effects to hard disc drives or the like.
In order to achieve the object mentioned above, the present invention is directed to a pressure sensitive adhesive sheet comprising a base and a pressure sensitive adhesive layer provided on the base, wherein the content of silicone compound in the pressure sensitive adhesive sheet is equal to or less than 500 xcexcg/m2.
This makes it possible to provide pressure sensitive adhesive sheets which are hard to give adverse effects to hard disc drives or the like.
Preferably, in the pressure sensitive adhesive sheet of the present invention, the amount of gas generated from the pressure sensitive adhesive sheet at a temperature of 85xc2x0 C. for 30 minutes is equal to or less than 20 mg/m2. This makes it possible to prevent occurrence of the adverse effects to the hard disc drives or the like more reliably.
In the present invention, it is preferred that the sum of amounts of NOxxe2x88x92, Clxe2x88x92, PO43xe2x88x92, K+, Fxe2x88x92, Na+ and Ca2+ contained in the pressure sensitive adhesive sheet is equal to or less than 20 mg/m2. This also makes it possible to prevent occurrence of the adverse effects to the hard disc drives or the like more reliably.
Further, it is also preferred that the base is formed from a plastic film or a lint free paper. This makes it possible to prevent generation of particles or the like more effectively, and therefore it becomes possible to prevent occurrence of the adverse effects to the hard disc drives or the like more reliably.
Furthermore, in the pressure sensitive adhesive sheet of the present invention, it is also preferred that an antistatic layer is provided between the base and the pressure sensitive adhesive layer. This makes it possible to effectively prevent generation of electrification at peeling-off of the pressure sensitive adhesive sheet from the release sheet. Further, even in the event that voltage is generated around the attaching portion of the pressure sensitive adhesive sheet, it can be grounded safely.
In this case, it is preferred that the antistatic layer includes at least one antistatic agent selected from the group consisting of carbon black, metal-based conductive filler, metal oxide-based conductive filler and xcfx80 electron conjugated conductive polymer. This makes it possible to effectively prevent transfer of ions to an adherend, and thereby poor connection and deterioration of performance in the hard disc drive can be prevented more effectively.
In this case, it is also preferred that the antistatic layer is composed of a thin film of a metal or metal oxide. This makes it possible to effectively prevent transfer of ions to an adherend, and thereby poor connection and deterioration of performance in the hard disc drive can be prevented effectively.
Furthermore, it is also preferred that the surface resistivity of the antistatic layer is in the range of 1xc3x97104xe2x88x921012 xcexa9. This makes it possible to effectively prevent generation of electrification at peeling-off of the pressure sensitive adhesive sheet from the release sheet. Further, even in the event that voltage is generated around the attaching portion of the pressure sensitive adhesive sheet, it can be grounded more safely.
Another aspect of the present invention is directed to a pressure sensitive adhesive sheet with a release sheet which comprises the pressure sensitive adhesive sheet as described above and a release sheet attached to the pressure sensitive adhesive sheet, the release sheet having a release agent layer. This makes it possible to provide a pressure sensitive adhesive sheet with a release sheet which hardly gives adverse effects to hard disc drives or the like.
In this case, it is preferred that the count of generated particles having a diameter of 0.1 xcexcm or more generated from the pressure sensitive adhesive sheet with a release sheet is equal to or less than 100 particles/liter. This makes it possible to prevent generation of particles that are liable to give adverse effects for reading and writing data.
Further, it is also preferred that the releasing agent layer is formed of a material containing an olefin-based thermoplastic elastomer and a polyethylene resin. This makes it possible to effectively prevent an environment in which silicone compound is transferred into the pressure sensitive adhesive layer from being produced in the pressure sensitive adhesive sheet with release sheet, as well as to obtain excellent reliability.
Furthermore, it is also preferred that the weight ratio of the olefin-based thermoplastic elastomer with respect to the polyethylene resin is in the range of 25:75 to 75:25. This makes it possible to obtain especially excellent reliability and heat resistance.
Moreover, it is also preferred that the density of the olefin-based thermoplastic elastomer is in the range of 0.80 to 0.90 g/cm3. The also makes it possible to obtain especially excellent reliability and heat resistance.
These and other objects, structures and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and examples.